Figure 8 . Distribution of warm-water and cold-water organisms in the 0-100 m. layer in 

 1952. ® Warm-water organisms . o Cold-water organisms . 



It appears that this is mainly due to the submarine ridge known as Mohn's Threshold-; In 

 some places, Mohn's Threshold has large eminences alternating with hanks, above which rise caps 

 of cold water, forming a sort of barrier which holds back the warm-water plankton fauna, hindering 

 its northward movement. 



An interesting biological feature of certain plankton organisms in the North Atlantic is the 

 fact that individual species that inhabit the hi^ latitudes and constitute the bulk of the zooplankton 

 there are also found in considerable quantities in the central areas of the Norwegian Sea, normally 

 at great depths, where the temperatures are low (0-l°C) and the salinity reduced (less than 35 /oo). 

 Among these organisms are Dimophyes arctica, Calanus hyperboreus , Pareuchaeta norvegica, P. 

 glacialis , Metridia longa, Scolocithrix minor , Clione limacina , Sagltta elegans, Eukrohnia hamata 

 and Oikopleura labradoriensis . 



]_/ A natural frontier in the north of the Norwegian Sea running in a north-easterly direction 

 from Jan Mayen to Bear Island . 



89 



